474 GYPSUM THE OPERATIVE INGREDIENT. 



same soil naturally, but not marled. Numbers 4, 5, and 6, were 

 from the pit dug in the beach, half a mile distant, apparently 

 similar to each other, and to the preceding specimens. All these 

 are of the dark stratum (Z)) richest in green-sand (except the 

 lowest, j), and all before rated by me as containing 50 per cent, 

 of the pure granules. Professor Rogers stated the same to contain 

 60 to 70 per cent. (See F. Register, vol. ii., p. 750.) Even if leaving 

 the green-sand out of consideration, and out of the estimate of 

 value, there would still remain enough of active manuring princi- 

 ples to produce a large share (at least) of the beneficial effects which 

 I have found from the use of this earth ; and I have heard of but 

 few other applications in Virginia, other than those made on Coggins 

 Point farm, and of none with different or better certain effects. 

 With the help of surplus carbonate of lime in the soil (furnished 

 by nature or by previous marling or liming), 100 bushels of this 

 earth, averaging in strength the ingredients of these specimens 

 analyzed by Professor Shepard, would furnish nearly 5 bushels of 

 pure sulphate of lime (gypsum) ; and 40 bushels to the acre would 

 furnish 2 bushels of sulphate of lime. Not one of these specimens 

 contained any gypsum visible to the eye ; and but one specimen 

 (number 9) contained any visible sulphuret of iron; and therefore 

 these ingredients may be fairly supposed to be at least as abundant 

 in the earth dug in any considerable operation. What the green- 

 sand or any other ingredients may do in addition, I pretend not to 

 estimate. But so far as I have learned from my own experience 

 and all known experience of other persons, the whole operation of 

 this earth, when used alone, is precisely of such kind as I would 

 anticipate from gypsum, though "yielding more of benefit in mea- 

 sure and value. Nor should I therefore be understood as placing 

 a low estimate on the value of the effects produced. Since seeing 

 the effects this year, and especially since having formed the opinion 

 that the upper and exposed parts (most generally used formerly) 

 are comparatively worthless and should be avoided, I count on 

 much benefit being derived from this manure, and am desirous that 

 it shall be largely used ; as my son and partner, and the sole 

 director of our farming, proposes to do for the next year's growth 

 of clover. Still, I am now as far as ever from believing in or ex- 

 pecting such great and regular benefit as would be inferred to be 

 certain from views and statements which rest upon the authority 

 of the former geological surveyor of Virginia.* 



* Professor Shepard, in the above letter, asserts the identity of the gra- 

 nules of " green-sand," with chlorite, or green talc. The proportions of 

 the constituents of chlorite are far from being uniform ; though the same 

 kinds are usually found, in various proportions. Of these, magnesia seems 

 to be always present. If so, may not this be an important manuring ele- 



